Stencil



Patented May 22, 1934 UNITED STATES LQBMZZ PATENT OFFICE 1,960,172, STENCIL a corporation of Delaware No Drawing. Application September 14, 1929,

. Serial No. 392,747

11 Claims.

This invention relates to improvements in stencils, and more particularly relates to the coating materials used for the sheets of the stencil.

By stencil in the following description and claims is meant a composite article embodying material normally impervious tov a printing ink, so that it then permits the passage of the ink at the treated points. The preferred form of stencils comprises the printing sheet proper, and a backing sheet assembled together in manufacture so that the two may be fed as a whole into, for example, a typewriting machine, and the types of this machine employed for displacing portions of the material from the printing sheet so that permeable portions are left in this printing sheet through .which the printing ink may pass: although obviously this displacement may also be accomplished by a stylus or similar instrument competent of forcing this. material out of the way. Usually,

the printing sheet comprises a piece of porous paper such as Yoshino or the like having a coating thereon.

It has heretofore been proposed to employ waxes, shellac, pyroxylin compound and the like for the making of dry stencils, that is, stencils which do not need a preliminary softening operation before being stencilized by a typewriter or stylus as noted above. Wax stencils are usually brittle, and liable to crack and thus permit smutting of the printed sheet at points other than those acted upon by the typewriter or stylus. Shellac stencils likewise are brittle and have such low drying properties that the cost of manufacture is very high. Pyroxylin stencils, i. e., those employing cellulose compounds as a base, are subject to serious deterioration, and are usually not of uniform quality.

In seeking to avoid the inconvenience of these prior proposals, it has been found that seed-lac furnishes a very satisfactory base for coating the printing sheet, if proper precautions and materials are employing inmaintainingitsplasticityand infacilitatingits drying, and for preserving it in its stencilizable condition.

Seed-lac in a pure commercial form is dissolved in an ether-alcohol mixture, and a small quantity of nitrate of cotton is added to facilitate the quick-drying of the mixture, so that it may be handled in a short time after coating upon the printing sheet. A suitable plasticizing agent to maintain .the lac in a flexible condition is then added, such as dibutyl phthalate or the like, and for this purpose it is preferred to employ tricresyl phosphate, particularly in the form of Lindol, (a commercial preparation sold on the market as a plasticizer by the Celluloid Corp. of America) in the proportion of 5 to 10% by weight of the lac. To this mixture is then added a small quantity of acetic acid (99% glacial acetic acid U. S. P.) which sets the color and prevents any excessive bleeding on of the coating compound onto or into the backing sheet, and assists in maintaining the 'stenciling coating soft and plastic. To this is then added a fatty acid, such as commercial white olein, with which has previously been mixed one-tenth of 5 one percent of alpha-naphthol.

It has been found that a-very successful stencil of long life may be produced by a coating com-, prising:

Seed-lam. 12 Pounds Cotton nitrate 1 Pounds Fatty acid 40 Pounds Acetic acid 8 Ounces Ether-alcohol solvent 46 Pounds 100 Pounds Another example of a coating composition, yielding a more flexible stencil, and'being of even greater drying capacity, is the following:

Seed-lac 14 Pounds Cotton nitrate. 4 Pounds Ether-alcohol solvent 180 Pounds Fatty acid Pounds Acetic acid 1 .Pound 85 Tricresyl phosphate 1 Pound Titre 12 to 15 C. Unsaponifiable matter 2.5 to 3.5% Free'fatty acid 97 to 99% as Oleic Iodine value 87 to 89%,. Color 2 to 3 N. P. A.

Free from mineral acid.

The alpha naphthol is employed to prevent oxidation of the fatty acid, and hence to preserve it while the stencil is being stored. To the fatty acid may be added, if desired, a proportion of vegetable or similar oil of low iodine value, to assist in preserving, the coating: as an example no 12 pounds of the fatty acid may be substituted'by olive and/or cocoanut oil in like quantity by weight.

It will be noted that the preferred fatty acid for employment is oleic acid, which is an'unsaturated carbon compound, and is normally liquid at ordinary temperatures: although mixtures may be employed which are similarly liquid or plastic, i. e., not hard or rigid, at the usual working temperatures for such stencils.

The coating composition comprises a solvent, a slowly hardening base (lac), a quickly hardening material (cotton nitrate) to establish a rapid initial setting so that the sheet maybe handled shortly after its immersion, a plasticizing agent (acetic acid with or without the addition of material such as lindol, dibutyl phthalate, etc.) to maintain the flexibility of the material and prevent cracking, and a fatty acid material which of itself is plastic at working temperatures; all of these ingredients preferably being soluble or emulsifiable in the single solvent.

Thewcomposition having been madeupin the form given, the Yoshino paper is immersed in the mixture and hung up to dry, whereupon the quick drying properties of the mixture of lac and mtrate of cotton rapidly causes a stiffening or hardening of the mixture so that the sheet may soon be handled and it is unnecessary to provide a large storage space for drying sheets. The fatty acid appears to form an emulsion with the mixture of lac, plasticizer and the cotton hardening agent. After the sheet is coated and dries, the acid is absorbed by the paper to a greater extent than the lac mixture, and also some of the fatty acid forms a surface coating on the outside of the coated sheet: so that ultimately the stencil'sheet comprises a sheet of paper saturated with amixture containing a large proportion of fatty acid coated on each side by a film comprising a mixture of a relatively high proportion of the lac mixture, which film in turn has a protecting coating of acid (with a small percentage of alpha-naphthol) on the exterior. In some instances, the separation of fatty acid from the lac mixture is very definite, so that there is a central sheet of paper saturated with fatty acid and coated with the lac mixture, while the lac mixture in turn is protected by a thin dressing of fatty acid. This results in a stencil sheet adequate to withstand a great deal of handling, and yet immediately stencilizable without preliminary softening.

In order to preserve the external fatty acid film, it is preferred to provide a special backing sheet which has been produced by oilinga sheet of stiff paper with an oil of low iodine value (i. e. a sub- It is obvious that other proportions of material and preparations thereof may be employed according to the specific properties of the selected ingredients, for the preparation of stencils which have the desired properties of plasticity and life.

I claim:

1. The combination in a stencil having a printing sheet with a stencilizable coating including oleic acid, of a backing sheet coated with neatsfoot oil and glycerine.

2. A stencil printing sheet comprising a porous base having a stencilizable coating thereon comprising lac, a cellulose ester soluble in a lac solvent, tricresyl phosphate and oleic acid.

3. A stencil printing sheet coating composition comprising lac, cellulose nitrate, a volatile solvent for said lac and cellulose nitrate, acetic acid, tricresyl phosphate, and a liquid higher fatty acid.

4. A stencil printing sheet comprising a porous base having a stencilizable coating thereon comprising lac, a liquid higher fatty acid, and alphanaphthol.

5. A stencil printing sheet comprising a porous base saturated with oleic acid, films on each side of the saturated sheet comprising a mixture containing lac, oleic acid, a plasticizer and a quickly hardening agent, and a coating of oleic acid with a small percentage of alpha-naphthol on the outside of each of said films.

6. A stencil printing sheet comprising a porous base having a stencilizable coating thereon comprising lac, a cellulose ester, acetic acid and a liquid higher fatty acid.

7. A stencil printing sheet comprising a porous base having a stencilizable coating thereon comprising lac, a lac plasticizer in the proportion of five to ten per cent of the lac, a cel1ulose ester soluble in a lac solvent in a proportion not ex-' ceeding thirty per cent of the lac, and liquid fatty acid.

8. A-stencil printing sheet comprising a porous base having a stencilizable coating thereon comprising lac, a lac plasticizer in the proportion of five to ten per cent of the lac, a cellulose ester soluble in a lac solvent in a proportion not exceeding thirty per cent of the lac, and a liquid higher fatty acid in quantity at least three times the combined lac and cellulose ester.

9. The combination in a stencil having a printing sheet with a stencilizable coating including oleic and acetic acid, of a backing sheet coated with a low-iodine-value oil and glycerine.

10. The combination in a stencil having a printing sheet with a stencilizable coating thereon comprising lac, a cellulose ester soluble in a lac solvent, a lac plasticizer, acetic acid and a'liquid higher fatty acid, of a backing sheet coated with a low-iodine-value oil and glycerine.

11. The combination in a stencil having a printing sheet with a stencilizable coating including a fatty acid, of a backing sheet having on the face toward the printing sheet a first coating of 

